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Session 84 - Neutron Stars and Their Friends.
Oral session, Thursday, June 13
Historical Society,
We study properties of an isolated quark-core neutron star in its spin-down process. We find that the central density of the star increases with time, and more neutron matter is converted into quark matter via continuous quark-hadron phase transition. As a result, the whole star contracts while its quark core increases in size and mass. This has two observational signatures: first, the fractional moment of inertia of the neutral component of the star (I_n/I) decreases and results in a decrease of the proportional healing parameter (Q) of pulsar glitches; second, due to the contraction of the whole star, the total moment of inertia decreases and results in an increase in the braking index (n) of the pulsar spin-down process. This makes the spin-down behavior of a quark-core neutron star different from that of ``pure'' neutron stars. In comparison, most previous work about rotational properties of neutron and quark stars concentrated on rotation-induced mass ``increase'', which is related to star families and not directly observable.
In the extreme case, catastrophic quark-hadron phase transition or pion condensation may happen to neutron stars at a rate of about 10^-6 yr^-1 per galaxy, with an energy release of about 10^52 ergs, and may be a good explanation of gamma-ray bursts (GRBs) at cosmological distances. If so, the detection of gravitational waves (GW) as counterparts of GRBs will be less likely than previously expected. We give an approximate light curve of GW for a catastrophic phase transition in a fast rotating star, and find it to be in sharp contrast to the predictions of neutron star merger models. We also discuss an extremely strong magnetic field that may be formed via the dynamo process during collapse; the effects of this field on electromagnetic and gravitational radiation; and an initial high energy neutrino burst due to the production of strange quarks.
